I train taekwondo and I don't know what to do. I have to fight against someone taller, with longer legs than me. If I get too close, they either hit me or push me away. They can still kick me when I'm too far away to kick them. Do you know some kind of trick I could use.
They will continue to be able to stop you with a lead leg sidekick if they control your range. You can bait them to kick by footwork, faking, or by offering a target (i.e. Squaring your body to them) then evading (stepping out at an angle) and countering (round kick to body, crescent kick to head).You will need good footwork to avoid their technique and get inside their range- hit them- then get back out. When I get inside a taller person's range I use a lot of quick punching before pulling back.
If you limit yourself to kicking, you're in trouble unless you're really fast.
Against a person who depends on long range kicks, i would normally try to get inside their range, or parry a kick nage-ashe to turn them around, come in close for kidney shots, then get out of range again before they recover their balance.
As ksp08 says, you need to have good footwork and be able to bait them effectively.